Field of the Invention
The invention relates to a method and a device for monitoring the setting of the phase between the pixel clock rate of a graphics card and the sampling clock rate of a flat screen having an analog interface.
Flat screens having an analog interface have to be adapted to the graphics card of the connected computer. If the phase or sampling frequency are set incorrectly, the picture is fuzzy and exhibits interference.
Whereas the values for picture position, that is to say the right-left and top-bottom setting, and the sampling frequency can be defined as preset values for standard modes, this is not possible for the phase since the phase depends on the graphics card used and also on the video line.
A microprocessor is usually provided in flat screens according to the prior art, the microprocessor performing the general control of the flat screen. This microprocessor is configured in such a way that it can also identify the video mode set at the computer. If the mode has already been set at the factory or by the user, the flat screen is operated with the stored settings for picture position, sampling frequency and phase. By contrast, if the mode is one which has not yet been implemented in the microprocessor of the flat screen, then standard values are adopted for picture position, sampling frequency and phase. These standard values are not satisfactory in all cases.
The setting of the sampling clock rate and of the phase has a direct effect on the picture quality. An optimum sampling frequency is given when the sampling of all the pixels of a line, for example, of a video signal ensues in a stable or characteristic region of the pixels, for example in the center of each pixel. The data conversion yields optimum results in that case. The picture shown has no interference and is stable. In other words, the optimum sampling frequency is equal to the pixel frequency. If an incorrect sampling frequency is set, for example if the sampling clock rate is too fast in comparison with the pixel clock rate, the pixels are initially sampled in the permissible region, that is to say in the center between two edges, but the subsequent pixels are sampled more and more in the direction of an edge until even the region between two pixels is sampled, which obviously leads to an unsatisfactory picture quality. Incorrect samples are derived in the region where the pixels are not sampled in an optimum, characteristic region. The picture then exhibits a high degree of vertical interference. The greater the difference in frequency between the sampling clock rate and the pixel clock rate, the more regions with vertical interference are visible on the screen.
However, even in cases in which the sampling clock rate is identical to the pixel clock rate, the picture quality can suffer if the phase is not set correctly. The reason is that the sampling takes place in a pixel region which is not ideally suited to sampling, for example too close to the front or back edge of a pixel. This problem can be solved by the phase, that is to say the sampling instant, overall being shifted until the sampling takes place in a characteristic or permissible region of the pixels. If the phase is not set correctly, the picture quality on the entire screen is impaired by noise signals.
Many users are unaware of the relationship between sampling frequency and phase with respect to the picture quality. If the picture is fuzzy, a defect is assumed and after-sales service is enlisted. This leads to unnecessary costs. Indications in the manual or on the packaging of the screen are overlooked by many users. Moreover, some users do not know that every resolution which is used and is set with respect to a graphics card requires a dedicated adjustment. If the picture quality is unsatisfactory for the reasons mentioned above, then in the most favorable case the after-sales service or the hotline of the manufacturer is contacted, whereupon the user is informed of the adjustment to be made to the phase. In some cases, however, entirely satisfactory monitors are returned under warranty even though only the phase must be set correctly.
Published, Non-Prosecuted German Patent Application No. DE 39 14 249 A1 discloses a method for a clock recovery from an input signal generated with an unknown clock, in which the input signal is digitized with a comparison clock in different phase angles. From the profile of the phase angle (input signal to comparison clock), the difference between the clock frequency of the input signal and that of the comparison clock is determined and the frequency of the comparison clock is corrected accordingly.
Published, Non-Prosecuted German Patent Application No. DE 19 751 719 A1 describes a signal processing method for an analog picture signal. In this case, the analog picture signal originates from a computing unit in which the signal has been generated digitally in accordance with a graphics standard, such as e.g. EGA (enhanced graphics adapter), or VGA (video graphics array), and has subsequently been converted into analog form. The method subjects the analog picture signal to an analog/digital conversion with a first, chosen sampling frequency, after which the sampled picture is then investigated for picture disturbances in order to determine a corrected sampling frequency. Further measures relate to the determination of the optimum sampling phase and the determination of the exact position of the active picture relative to the horizontal and vertical synchronizing pulses.
It is accordingly an object of the invention to provide a method and a device for monitoring the setting of the phase in flat screens which overcome the above-mentioned disadvantages of the heretofore-known methods and devices of this general type and which ensure that the required setting of the phase is performed whenever such a setting or adjusting is required.
With the foregoing and other objects in view there is provided, a method for monitoring, in a flat screen/graphics card/computer system, a setting of a phase between a pixel clock rate of a graphics card and a sampling clock rate of a flat screen having an analog interface, the method includes the steps of:
setting a flag if a phase of a flat screen has been set from a user-side;
interrogating the flag upon switching on the flat screen and/or switching a video mode at a computer and/or exchanging a graphics card and/or exchanging the computer; and
providing a display indication or initiating a setting of the phase if, during the interrogating step, it is ascertained that the flag is not set.
In other words, the method according to the invention is characterized in that a flag is set if the phase of the flat screen has been set by the user, in that the flag is interrogated upon a switch-on of the flat screen and/or upon a changeover of the video mode at the computer and/or an exchange of the graphics card and/or upon an exchange of the computer, and in that a display is provided or a setting of the phase is initiated if, during the interrogation, it is ascertained that the flag is not set. In other words, in addition to the settings which are already stored for each mode, a flag is also inserted which is set as soon as the phase has been set by the user. As a result, the user is not just informed by manuals and other accompanying material of the necessity of effecting phase setting, rather the user is, as it were, compelled to perform the phase setting whenever this is necessary.
If the flat screen is switched on and/or the video mode of the computer is changed over, the processor situated in the flat screen will interrogate the flag stored with respect to the present mode. If the flag is set, that is to say that the flat screen has already been set to the user""s system, further operation of the system would proceed as usual. By contrast, if the flag has not yet been set, the flat screen shows a reaction, and a corresponding display takes place or automatic setting of the phase is initiated.
One advantageous embodiment of the method according to the invention is characterized in that the flag is cleared after a change in the video mode at the computer and/or an exchange of the graphics card and/or an exchange of the computer. In the case of new monitors from the factory, the flags must be cleared for all preset modes, since the phase has not yet been set to the user""s system. This advantageous embodiment of the method according to the invention can encompass not just these cases but also any alteration to the system which necessitates a phase adjustment. The same applies, of course, also to modes for which there is as yet no presetting in the flat screen.
A further advantageous embodiment of the method according to the invention is characterized in that the flag is set or cleared in a microprocessor in the flat screen, in which case the display is advantageously output via the OSD (on screen display). As a result, the existing hardware is utilized, and costs are saved.
A further advantageous embodiment of the method according to the invention is characterized in that after the setting of the phase and upon identification of a mode change, a check is made to determine whether a line, but at least the first line, above the picture region and/or below the picture region and/or a column, but at least the first column, of the front porch region and/or of the back porch region is/are xe2x80x9cblackxe2x80x9d, and in that the flag is set only when the check yields a positive result. It is thus possible to check the phase setting performed by the user, and the user is informed if the phase setting performed is not optimal.
A further advantageous embodiment of the method according to the invention is characterized in that automatic setting of the phase is initiated. In contrast to manual setting of the phase, automatic phase setting is advantageous for many inexperienced users.
An advantageous embodiment of the method according to the invention is characterized in that the rising edge of a video pulse of a sufficiently bright pixel is determined, in that the falling edge of the video pulse in a sufficiently bright pixel is determined, and in that the phase is set in such a way that the sampling instant is located approximately in the center between the rising and falling edges of a video pulse.
Another advantageous embodiment of the method according to the invention is characterized in that the rising edge of a video pulse of a sufficiently bright pixel is determined, and in that the phase is set in such a way that the sampling instant is shifted approximately by half a pixel width in the direction of the pixel center.
A further advantageous embodiment of the method according to the invention is characterized in that the falling edge of the video pulse in a sufficiently bright pixel is determined, and in that the phase is set in such a way that the sampling instant is shifted approximately by half a pixel width in the direction of the pixel center.
Whereas the picture-position and the sampling frequencies can be determined relatively simply through the use of an algorithm and be set accordingly, the phase angle or phase relationship is more difficult to determine. The three exemplary embodiments of the method according to the invention mentioned last are simple and satisfactory methods for setting the phases.
An advantageous embodiment of the method according to the invention, wherein the picture region with the pixels on the flat screen is provided in lines and columns between a back porch region and a front porch region, is characterized in that a pixel in the first picture column next to the back porch region is selected as the sufficiently bright pixel for the determination of the rising edge and a pixel in the first picture column next to the back porch region is selected as the sufficiently bright pixel for the determination of the falling edge. The method can be embodied particularly well if the most pronounced edges are evaluated or if adjacent regions or dots have a greatly different brightness. Therefore, a dot or point respectively in the first or last picture column is particularly well suited since, in combination with the front or back porch region, respectively, it completely satisfies the required conditions and can be found with relatively little outlay.
In the case of automatic phase angle setting or phase position setting, special test patterns having alternately white and black pixels are usually required in previous flat screens having an analog interface, the test pattern having to be displayed by the graphics card. This has the disadvantage that software has to be installed on the computer and started, and that, moreover, the software has to be available for all customary operating systems. By contrast, the above-described advantageous embodiment of the method according to the invention has the advantage that no such test pattern and no corresponding software are necessary in order to carry out the automatic phase setting.
An advantageous embodiment of the method according to the invention is characterized in that the brightness of a plurality of pixels of the first and of the last picture column, respectively, is measured and the pixels having the greatest brightness in the first and last picture column, respectively, are selected for the determination of the rising and falling edge, respectively, of the video pulse. This ensures that pixels having sufficiently pronounced edges are used for the measurement.
An advantageous embodiment of the method according to the invention is characterized in that firstly the pixels (nxc3x97k), where n=1, 2, . . . N and k=constant, for example 10, are measured, and in that, if a sufficiently bright pixel has not been found, the pixels (n+m)xc3x97k where m=1, 2, . . . N, are measured until a sufficiently bright pixel is found. As a result, a search for suitable pixels is carried out efficiently and in a short time.
An advantageous embodiment of the method according to the invention is characterized in that in order to determine the amplitude value of the pixel, the phase is shifted until the measured amplitude values no longer change significantly, and in that the amplitude value then determined is then processed further.
As an alternative, one advantageous embodiment of the method according to the invention is characterized in that the phase used during the determination of the amplitude value is advanced until the measured amplitude values are less than a predetermined limit value, for example less than 50% of the amplitude value, in that the phase is delayed by half a dot width or pixel width, and in that the amplitude value which is then measured is processed further.
The two embodiments of the method according to the invention mentioned last are simple solutions for determining the brightness of the pixel, as a precondition for determining the position of the rising and falling edges of the pixel.
A further advantageous embodiment of the invention is characterized in that, in order to determine the rising edge, the phase is shifted in the direction of the back porch region until the measured amplitude value falls to a predetermined percentage, for example 50%, of the amplitude value determined beforehand, and in that this value of the phase is buffer-stored as the location of the rising edge.
Moreover, another advantageous embodiment of the invention is characterized in that, in order to determine the falling edge, the phase is shifted in the direction of the front porch region until the measured amplitude value falls to a predetermined percentage, for example 506, of the amplitude value determined beforehand, and in that this value of the phase is buffer-stored as the location of the falling edge. In this way, the rising and falling edges of two pixels are determined in a simple manner, and the phase can then be set with a magnitude such that it lies between the rising and falling edges, approximately in the center of a pixel.
According to another mode of the invention, the phase or the sampling instant is delayed relative to the center between the rising and falling edges by a predetermined amount, for example 10% of the pixel width.
With the objects of the invention in view there is also provided, in a system including a computer, a graphics card operating with a pixel clock rate, and a flat screen with an analog interface and operating with a sampling clock rate, a device for monitoring a setting between the pixel clock rate and the sampling clock rate, including:
a microprocessor for setting a flag if a phase of the flat screen has been set from a user-side;
the microprocessor performing an interrogation of the flag upon switching on the flat screen and/or switching a video mode at the computer and/or exchanging the graphics card and/or exchanging the computer; and
the microprocessor initiating a display indication and/or a setting of the phase, if the interrogation ascertains that the flag is not set.
In other words, the device for monitoring the setting between the pixel clock rate of a graphics card and the sampling clock rate of a flat screen having an analog interface in a flat screen/graphics card/computer system, is characterized by a microprocessor which is configured in such a way that a flag is set if the phase of the flat screen has been set by the user, in that the flag is interrogated upon a switch-on of the flat screen and/or upon a changeover of the video mode at the computer and/or an exchange of the graphics card and/or upon an exchange of the computer, and in that a display is provided or a setting of the phase is initiated if, during the interrogation, it is ascertained that the flag is not set. The simplicity of the device shows that the invention can be implemented with extremely simple measures and in a highly effective manner.
According to another feature of the invention, a setting device is provided for initiating an automatic setting of the phases.
A further advantageous embodiment of the device according to the invention is characterized by a device which determines the rising edge of a video pulse of a sufficiently bright pixel for example in the first picture column next to the back porch region, a device which determines the falling edge of the video pulse in a sufficiently bright pixel in the last picture column next to the front porch region, and a setting device which sets the phase in such a way that the sampling instant is located approximately in the center between the rising and falling edges of a video pulse.
According to another feature of the invention, there is provided a device which determines the rising edge of a video pulse of a sufficiently bright pixel in the first picture column next to the back porch region, and a setting device which sets the phase in such a way that the sampling instant is shifted approximately by half a pixel width in the direction of the pixel center.
According to yet another feature of the invention, there is provided a device which determines the falling edge of the video pulse in a sufficiently bright pixel in the last picture column next to the front porch region, and a setting device which sets the phase in such a way that the sampling instant is shifted approximately by half a pixel width in the direction of the pixel center.
According to a further feature of the invention, there is provided a device for shifting the phase in order to determine the sample or sampling value of the pixel until the measured amplitude values no longer differ significantly, the sample which is then determined being processed further.
According to another feature of the invention, there is provided a device which advances the phase used during the determination of the sample until the measured amplitude values are less than a predetermined limit value, for example less than 50% of the sample, and by a device which then delays the phase by half a pixel width, the sample which is then measured being processed further.
According to yet another feature of the invention, there is provided a device which shifts the phase, for the purpose of determining the rising edge, in the direction of the back porch region until the measured amplitude value falls to a predetermined percentage, for example 50% of the amplitude value determined beforehand, this value of the phase being buffer-stored as the location of the rising edge.
According to a further feature of the invention, there is provided a device which shifts the phase, for the purpose of determining the falling edge, in the direction of the front porch region until the measured amplitude value falls to a predetermined percentage, for example 50% of the amplitude value determined beforehand, this value of the phase being buffer-stored as the location of the falling edge.
Other features which are considered as characteristic for the invention are set forth in the appended claims.
Although the invention is illustrated and described herein as embodied in a method and a device for monitoring the setting of the phase in flat screens, it is nevertheless not intended to be limited to the details shown, since various modifications and structural changes may be made therein without departing from the spirit of the invention and within the scope and range of equivalents of the claims.